Clarify ambiguous reference error message

[som-snytt]

Fixes #12682

Name binding is tricky because of the intersection of binding precedence and scope.

I think this states the matter most succinctly: Lower precedence cannot shadow higher.

Also modernized the syntax.

It's arguably weird for the compiler to refer to itself in the third person:

The compiler can't decide which of the possible choices you are referencing

Less nerdy and more former schoolmarm:

to which of the possible choices you could possibly be referring

[som-snytt]

@dwijnand please review? Surprisingly difficult rebase over refactor of messages.scala, so if it is not accepted, I will drop it.

[dwijnand]

LGTM, sorry you waited this long... :(

I have a question, but I don't mind merging this without that change.

[dwijnand]

Should we change this?

Suggested change

	| - Names introduced by imports
	| - Named imports take precedence over wildcard imports
	| - Names introduced by named imports
	| - Names introduced by wildcard imports

[som-snytt]

Yes. I was trying to strike a balance of informality.

[som-snytt]

Added a commit which finds words for Names introduced by import of a specific name. (Where "specific" means "specified".)

"Named import" is too brief to ring with clarity.

There must be a grammatical term for "by import" (similar to "call by name"), as opposed to "by imports" or "by importing".

The follow-up also restores the previous words in the note: the rule of thumb that defs are preferred to imports, and the special mention of the "new" rule, with a clause explaining when it is relevant:

+        | - Definitions in an enclosing scope take precedence over inherited definitions,
+        |   which can result in ambiguities in nested classes.

Thanks, Dale, for the nudge. No one will say, We didn't adopt Scala 3 because of that stupid message, but I must believe that a collective, cumulative effort must make a difference, not only in aggregate but in the life of some Scala learner yet unborn.

[SethTisue]

I must believe that a collective, cumulative effort must make a difference, not only in aggregate but in the life of some Scala learner yet unborn.

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